It is often desirable to shoot smaller caliber ammunition from a larger caliber firearm, thereby reducing the cost of the ammunition utilized, as well as possibly reducing felt recoil and/or noise during practice. In the case of a .22 caliber firearm, inexpensive rimfire ammunition may be utilized in firearms that were originally designed for centerfire ammunition by utilizing an appropriate conversion unit. Additionally, in the case of a rifle having separate upper receiver and lower receiver portions, for example, an AR-15 or M-16 type rifle, the upper receiver and barrel (hereinafter upper receiver assembly) can be separated from the lower receiver, and replaced with an upper receiver assembly of a different caliber. In either case, it is necessary to utilize a magazine designed for the smaller caliber ammunition within the magazine well that was designed for magazines holding larger caliber ammunition.
One adapter for use with a conversion assembly for utilizing .22 long rifle ammunition in an AR-15 rifle chambered for 5.56 mm. ammunition is disclosed in U.S. Pat. No. 8,387,296, issued to J. L. Overstreet et al. on Mar. 5, 2013. This adapter includes an actuator housing that fits at the top of the magazine well of a rifle, being secured between the upper receiver and lower receiver. The actuator housing defines a rectangular opening for receiving the top portion of a magazine, including the feed lips. A bolt catch actuator is slidably mounted in a rear portion of the actuator housing. The actuator includes a tab for engaging the rear portion of the follower of the magazine, and a rear portion for engaging the bolt catch on the rifle. This adapter relies on a magazine having a two-piece follower, with a main portion and an upper displaceable portion secured to the main portion. The upper displaceable portion is spring-biased rearward, so that upon the upper displaceable portion reaching the top of the magazine after the last cartridge is expended, the upper displaceable portion moves rearward under spring pressure to a position wherein it can engage the tab of the bolt catch actuator. By securing the base between the upper and lower receivers, which typically fit close together, there is some difficulty in securing the upper receiver to the lower receiver, as well as the potential for some stress on the forward screw and rear pin securing the two receiver portions together.
A similar adapter is disclosed in US 2011/0247483, filed by J. L. Overstreet et al. and published on Oct. 13, 2011. This adapter includes an actuator housing that fits at the top of the magazine well of a rifle, being secured between the upper receiver and lower receiver. The actuator housing defines a rectangular opening for receiving the top portion of a magazine, including the feed lips. A bolt catch actuator is slidably mounted in a rear portion of the actuator housing. The actuator includes a tab for engaging the rear portion of the follower of the magazine, and a rear portion for engaging the bolt catch on the rifle. As with U.S. Pat. No. 8,387,296, by securing the base between the upper and lower receivers, which typically fit close together, there is some difficulty in securing the upper receiver to the lower receiver, as well as the potential for some stress on the forward screw and rear pin securing the two receiver portions together.
U.S. Pat. No. 4,139,958, issued to J. P. Foote on Feb. 20, 1979, discloses a caliber conversion system for M-16 and AR 15 rifles. The conversion system includes a bolt/receiver assembly which replaces the bolt carrier of the rifle. The conversion system includes a magazine assembly which can be inserted into a standard M-16 or AR 15 magazine. The conversion bolt includes a groove on its right side for manual retraction of the bolt. Alternatively, the bolts may be manipulated using the rifle's charging handle. The bolt of the conversion unit is structured so that it may be held rearward by the rifle's bolt catch. The bolt may therefore be manually locked back using the rifle's standard bolt catch. However, the bolt will not automatically locked to the rear upon firing the last cartridge within the magazine, as would occur when the rifle's standard caliber ammunition is being used.
U.S. Pat. No. 4,079,555, issued to R. E. Elbe et al. on Mar. 21, 1978, discloses a magazine for a rimfire adapter for a centerfire firearm. The magazine cavity is positions to the rear of the magazine, positioning the base of the shorter cartridge in the same position as the base of the original cartridge.
U.S. Pat. No. 5,556,488, issued to E. Y. Yapp on Oct. 22, 1996, discloses an adapter for a semiautomatic handgun that was originally designed to accept double column magazines. The adapter facilitates the use of single column magazines. And adapter for a similar purpose is disclosed within U.S. Pat. No. 5,555,661, issued to E. Y. Yapp on Sep. 17, 1996.
Smith & Wesson currently manufactures and AR 15 style rifle in .22 lr. caliber, known as the M&P15-22. This rifle utilizes a magazine having an upwardly extending rear projection for activating the bolts catch on this rifle. However, in the absence of an appropriate adapter, this magazine is only useful in the rifle for which it was originally designed. It would be desirable to utilize this magazine with rifles utilizing .22 lr. upper assemblies, as well as rifles utilizing .22 lr. conversion kits.
Regardless of whether training occurs with the original caliber or with a smaller caliber, maintaining the original operation and manipulation of the rifle is critical to maximizing the value of the training. For example, training to perform fast reloads requires the ability to manipulate the rifle in the original manner in order to accomplish the reload. Therefore, automatically holding open the bolt utilizing the bolts catch after the last round in the magazine has been fired is important for accurate training. Furthermore, reloading the rifle utilizing the bolt catch and other original controls is important for training in proper reloading procedure. Reloading is one of many examples where maintaining the original functioning of the weapon while installing a conversion unit is critical.
Accordingly, there is a need for a magazine adapter for use with upper assemblies and caliber conversion units that activates the standard bolt catch on the rifle upon the firing of the last cartridge within the magazine. There is a further need for a magazine adapter that facilitates the use of all original controls on the rifle. There is an additional need for a magazine adapter that is usable with a wide variety of upper assemblies and conversion units. Furthermore, there is a need for a magazine adapter that is securely held in place within the rifle, yet may be easily installed and removed within the rifle. There is a need for a magazine adapter that does not place unnecessary stresses on the rifle with which it is used. Lastly, there is a need for a magazine adapter that may be utilized with multiple rifle systems, including those that may not necessarily utilize separable upper and lower receiver portions.